Cast film processes are well known for the manufacture of polyethylene film and the like. In such a process, molten polyethylene is generally conveyed by an extruder through an adaptor, into a slit-type die.
The die is so positioned adjacent to a main cooling roll, that the molten web emerging between the die lips contacts a water-cooled roll on a tangent to the roll surface. The speed of this first roll determines the take-off rate, and other rolls in the system are generally matched to this speed. Although the major share of cooling is accomplished on the main roll, auxiliary cooling rolls are often also used.
Cast film processes have generally not been used to produce amorphous films or toughened amorphous films. Such films generally must be oriented to improve the structural integrity of the film (prevent unwanted splitting during the manufacturing process and thereafter). Such orientation needs are problematic in a cast film processes, because over-orientated film will generally age prematurely and may have splitting problems during and after manufacture, particularly when over-orientation is in the MD or machine direction.
Prior to the present invention, it is believed that the industry did not have an understanding as to how amorphous (i.e., amorphous polyester or toughened amorphous polyester) films could be easily processed without encountering the above problems.